Engine Temperature Issue - Please Help!
Out of no where (at 154,000 miles), I noticed that in 100 degree temperatures, my engine temperature gauge that normally hits the halfway mark and stays there rather quickly (like within a couple minutes of running), started fluctuating and showing cool and sometimes nearly on cold. I was getting erratic (never hot) temperature gauge readings over the weekend. Once I would drive on the highway or have it running for a good while, it would rise to the midway mark like normal but if I were to go into say the convenience store (keeping in mind it's 100 degrees out) and then come back out after 5 minutes and start it back up, the gauge is back down there near the damn cold line. Obviously, after having the car for 154,000 miles, I know this isn't the case, the engine is blazing hot like always.
Ok so things to most likely rule out:
-Air bubble in coolant. Yes, I had changed two coolant hoses a couple weekends ago as preventative maintenence. Of course I purged a lot of old coolant in the process but filled up the cooling system and burped the car like I have done before. Additionally, the car has been driven about 1,000 miles since then and checked for air in the radiator and topped off like I have done numerous times previously.
-Bad Engine Coolant temperature sensor. This part is brand-new as a month ago. Keeping in mind that my old ECT sensor was completely busted (as in the top connector part spun freely independently of the metal nut part that screws into the head). Even when my old ECT sensor was bad, I was still getting the engine temperature to read correctly. The engine temp gauge must get a signal from some other temperature sensor.
-Thermostat. The engine had a new thermostat installed when I had the new engine installed at 109,000 miles. It's a factory Mazda thermostat. Additionally, if a thermostat was stuck open, I don't see how the coolant could be at the midway point (according to the gauge) and then after being shut off for 5 minutes, show COLD.
Now, one piece of additional info. is that my check engine light did come on once during this little mystery and the code was for "insufficient coolant temperature for stable operation" which makes sense. So the question becomes, is there another sensor somewhere that sends the engine temperature to the gauge? It must not be the ECT sensor because mine was completely broken in the past and my temperature gauge still functioned correctly.
I would definitely appreciate some help guys. I'll also confirm, with my AP, that my ECT is around 200 like it normally is. I would expect the ECT will be 200 even though the gauge will read cool or even COLD.
'06 Black Mica Mazdaspeed 6 GT (SOLD!)
P3 BUILT Engine w/BSD, Spec 2+ Clutch, BNR Stage 3 turbo, HKS SSQV BOV, HKS Twin-Power Ignition, HPFpump w/KMD internals, Saikou Catch Can, Driver's Wheel Well Vent Cover, R1 Concepts Slotted Rotors. Cobb Accessport tuned at 24 psi w/3 Bar MAP
CP-E: Rear Mount, DeltaCore FMIC, Downpipe, SafeSeal Injector seals VentPod w/VEI boost guage, Magnaflow Catback Exhaust, JBR 3.5" Full Intake, VCTS Delete, Redline Synthetic Gear Lubes, Battery Relocated to Trunk
Last edited by mczimer; 09-12-2011 at 12:28 PM.